Conventionally, percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA) have been widely used for treatment (expansion) of a narrowed site, obstruction site, or the like site of an intravascular lumen so as to restore or improve a bloodstream in a coronary artery, a peripheral vessel, or the like.
An example of general PTCA employing a balloon catheter is described below. First, a guiding catheter is inserted from a puncture site in a femoral artery, a brachial artery, or a radial artery. The guiding catheter is then inserted more deeply into an aorta, until a distal end of the guiding catheter is positioned at an entrance to a coronary artery. Next, a guide wire, which extends through a guidewire lumen, is inserted into the coronary artery until a distal end of the guide wire is positioned beyond the narrowed site of the coronary artery. Then, the balloon catheter is inserted along the guide wire so that a balloon of the balloon catheter is positioned at the narrowed site. Thereafter, the balloon is inflated by pressure fluid which is supplied, via an inflation lumen, from a device such as an indeflator. The balloon thus inflated expands the narrowed site. After the narrowed site is expanded, the balloon is deflated by reducing pressure inside the balloon, and then removed from the living body. In this way, PTCA is completed.
For a lesion such as that having a severely narrowed site or a chronic total obstruction, it may be impossible to insert the guide wire so that its distal end is positioned beyond the narrowed site. Accordingly, it may be impossible to treat such a lesion. If this is the case, a microcatheter or a penetration catheter is used. These catheters make it possible to insert the guide wire until the distal end thereof is positioned beyond the narrowed site.
Further, in performing PTCA, it may be necessary to locally administer a therapeutic agent to the narrowed site. An example of such a treatment is a treatment whereby to locally administer a thrombolytic agent to the narrowed site so as to lyse a thrombus. In performing this treatment, an infusion catheter is used. The infusion catheter is capable of locally administering the therapeutic agent to the narrowed site.
Among lesions to be treated by using a medical expansion catheter, specific lesions are a chronic total obstruction (CTO) lesion in the coronary artery, a lesion at a sharp bifurcation, a lesion at an entrance to a bifurcation, and the like. For such lesions, it is extremely difficult to insert the guide wire so that the distal end thereof is positioned beyond an affected site prior to the expansion treatment.
In order to treat the above specific lesions by inserting the guide wire, it is required to design the catheter in a devised manner so that the distal end thereof can be actively bent.
Patent Literature 1 discloses a catheter having an bending part at a distal end of an insertion section, wherein the bending part is driven by an operation wire extending from a distal end to a proximal end of the catheter. However, when the catheter is inserted into a peripheral vessel having a sharp curve, the catheter is deformed and thus the operation wire is subjected to large friction resistance. Accordingly, it may be impossible to manually operate the bending part in a desired manner.
In order to solve this problem, there have been considered a variety of methods for actively driving the distal end of the catheter without using the operation wire.
Patent Literature 2 discloses a medical tube having a movable part, which is bent by using pressure fluid. The movable part is bent by making use of a difference between a length of part of the balloon and a length of another part of the balloon, which difference occurs when the pressure fluid is injected into the medical tube. That is, the movable part of the medical tube is bent by (i) generating partial force in a long axis direction of the medical tube and (ii) making use of the force thus generated. However, since the balloon expands both in the long axis direction and a short axis direction, it is not possible to efficiently generate the force in the long axis direction of the medical tube. In addition, an external diameter of the movable part increases as an angle at which the movable part is bent becomes sharp.
Patent Literature 3 discloses an actuator constituted by (i) a noncircular tube that is elastically deformable and (ii) a member that is not so elastically deformable as the noncircular tube. The noncircular tube and the member are provided along with each other in an axial direction so as to form an integral structure of the actuator. The actuator is bent so that the member is positioned inside the noncircular tube, by adjusting pressure in the noncircular tube. However, the feature of the actuator disclosed in Patent Literature 3 lies in a shape of the noncircular tube, and thus the noncircular tube is limited as to its shape. Therefore, in a case where the actuator is put into medical use for example as a constituent part of the catheter, the actuator may damage a blood vessel or may be inconvenient for use because of its specified external diameter etc.
Patent Literature 4 discloses a cylindrical catheter that can be moved by using the pressure fluid. The catheter has a movable part, inside of which an aperture of a tube is positioned. The aperture of the tube can be operated by making use of force in the long axis direction of the catheter. More specifically, the catheter disclosed in Patent Literature 4 includes an elastic tube and an expansion controlling body for controlling expansion of the elastic tube. The elastic tube is provided uniformly inside the expansion controlling body. That is, the expansion controlling body is provided so as to cover an outer surface of the elastic tube. However, it is not possible to surely specify a direction in which the catheter is bent with use of the above two bodies alone. Therefore, the catheter of Patent Literature 4 further includes a cord-like body, which specifies the direction in which the catheter is bent.
However, in the catheter of Patent Literature 4, a position of the tube provided inside the movable part is unstable with respect to a position of the catheter. Accordingly, the tube may hinder the movable part from being bent, thereby hindering efficient movement of the catheter. Further, the expansion controlling body, which controls the tube from expanding in the short axis direction due to injection of the pressure fluid, is not optimized so that the tube is easily expanded and contracted in the long axis direction. Accordingly, the expansion controlling body is not capable of efficiently transducing expansion force of the balloon into force in the long axis direction. Therefore, the movable part cannot firmly keep a bent shape.